Fatwood is great stuff. I never go in the woods without some. The little saw I made if from a magnesium bar that was cut in half.
For regular use, I would go with a larger ferro rod and some fatwood or cotton soaked in vaseline (my favorite). But the mag/ferro rod is a true survival tool. Make sure you know how to use it, then tuck it away where, if you really need it, it will be handy. You can coat the ferro rod with nail polish so it won't rust.
Here are several tricks on using it. First, you can scrape the magnesium into a cotton ball. It will stay right there. Second, you can make a dimple in your hat or hanky and it will stay right there in a pile. Third, scrape plenty and fourth, hold the striker still and move the ferro rod away from the magnesium pile so the air current from your hand doesn't blow the magnesium away.
For me, it's strictly a backup tool but I still practice with it. If you know where you can get some magnesium (like an old lawn mower deck, you can drill holes in it and save the shavings for tinder. I carry mine in a film canister. Magnesium will burn under water, eh?